package s3local

import (
	"context"
	"errors"
	"fmt"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/engine"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/pilorama"
	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/pkg/service/tree"
)

// treeServiceEngineWrapper implements the basic functioning of tree service using
// only the local storage engine instance. The node position and count is fixed
// beforehand in order to coordinate multiple runs on different nodes of the same
// cluster.
//
// The implementation mostly emulates the following
//
//   - https://git.frostfs.info/TrueCloudLab/frostfs-node/src/branch/master/pkg/services/tree/service.go
//   - https://git.frostfs.info/TrueCloudLab/frostfs-s3-gw/src/branch/master/internal/frostfs/services/tree_client_grpc.go
//
// but skips details which are irrelevant for local storage engine-backed clients.
type treeServiceEngineWrapper struct {
	ng   *engine.StorageEngine
	pos  int
	size int
}

type kv struct {
	k string
	v []byte
}

func (kv kv) GetKey() string   { return kv.k }
func (kv kv) GetValue() []byte { return kv.v }

type nodeResponse struct {
	meta     []tree.Meta
	nodeID   uint64
	parentID uint64
	ts       uint64
}

func (r nodeResponse) GetMeta() []tree.Meta { return r.meta }
func (r nodeResponse) GetNodeID() uint64    { return r.nodeID }
func (r nodeResponse) GetParentID() uint64  { return r.parentID }
func (r nodeResponse) GetTimestamp() uint64 { return r.ts }

func (s treeServiceEngineWrapper) GetNodes(ctx context.Context, p *tree.GetNodesParams) ([]tree.NodeResponse, error) {
	nodeIDs, err := s.ng.TreeGetByPath(ctx, p.BktInfo.CID, p.TreeID, pilorama.AttributeFilename, p.Path, p.LatestOnly)
	if err != nil {
		if errors.Is(err, pilorama.ErrTreeNotFound) {
			// This is needed in order for the tree implementation to create the tree/node
			// if it doesn't exist already.
			// See: https://git.frostfs.info/TrueCloudLab/frostfs-s3-gw/src/branch/master/internal/frostfs/services/tree_client_grpc.go#L306
			return nil, tree.ErrNodeNotFound
		}
		return nil, err
	}

	resps := make([]tree.NodeResponse, 0, len(nodeIDs))
	for _, nodeID := range nodeIDs {
		m, parentID, err := s.ng.TreeGetMeta(ctx, p.BktInfo.CID, p.TreeID, nodeID)
		if err != nil {
			return nil, err
		}
		resp := nodeResponse{
			parentID: parentID,
			nodeID:   nodeID,
			ts:       m.Time,
		}
		if p.AllAttrs {
			resp.meta = kvToTreeMeta(m.Items)
		} else {
			for _, it := range m.Items {
				for _, attr := range p.Meta {
					if it.Key == attr {
						resp.meta = append(resp.meta, kv{it.Key, it.Value})
					}
					break
				}
			}
		}
		resps = append(resps, resp)
	}

	return resps, nil
}

func (s treeServiceEngineWrapper) GetSubTree(ctx context.Context, bktInfo *data.BucketInfo, treeID string, rootID uint64, depth uint32) ([]tree.NodeResponse, error) {
	var resps []tree.NodeResponse

	var traverse func(nodeID uint64, curDepth uint32) error
	traverse = func(nodeID uint64, curDepth uint32) error {
		m, parentID, err := s.ng.TreeGetMeta(ctx, bktInfo.CID, treeID, nodeID)
		if err != nil {
			return fmt.Errorf("getting meta: %v", err)
		}

		resps = append(resps, nodeResponse{
			nodeID:   nodeID,
			parentID: parentID,
			ts:       m.Time,
			meta:     kvToTreeMeta(m.Items),
		})

		if curDepth >= depth {
			return nil
		}

		children, err := s.ng.TreeGetChildren(ctx, bktInfo.CID, treeID, nodeID)
		if err != nil {
			return fmt.Errorf("getting children: %v", err)
		}
		for _, child := range children {
			if err := traverse(child, curDepth+1); err != nil {
				return err
			}
		}
		return nil
	}

	if err := traverse(rootID, 0); err != nil {
		return nil, fmt.Errorf("traversing: %v", err)
	}

	return resps, nil
}

func (s treeServiceEngineWrapper) AddNode(ctx context.Context, bktInfo *data.BucketInfo, treeID string, parentID uint64, meta map[string]string) (uint64, error) {
	desc := pilorama.CIDDescriptor{
		CID:      bktInfo.CID,
		Position: s.pos,
		Size:     s.size,
	}
	mv, err := s.ng.TreeMove(ctx, desc, treeID, &pilorama.Move{
		Parent: parentID,
		Child:  pilorama.RootID,
		Meta:   pilorama.Meta{Items: mapToKV(meta)},
	})
	return mv.Child, err
}

func (s treeServiceEngineWrapper) AddNodeByPath(ctx context.Context, bktInfo *data.BucketInfo, treeID string, path []string, meta map[string]string) (uint64, error) {
	desc := pilorama.CIDDescriptor{
		CID:      bktInfo.CID,
		Position: s.pos,
		Size:     s.size,
	}
	mvs, err := s.ng.TreeAddByPath(ctx, desc, treeID, pilorama.AttributeFilename, path, mapToKV(meta))
	if err != nil {
		return pilorama.TrashID, err
	}
	return mvs[len(mvs)-1].Child, nil
}

func (s treeServiceEngineWrapper) MoveNode(ctx context.Context, bktInfo *data.BucketInfo, treeID string, nodeID, parentID uint64, meta map[string]string) error {
	if nodeID == pilorama.RootID {
		return fmt.Errorf("node with ID %d is the root and can't be moved", nodeID)
	}
	desc := pilorama.CIDDescriptor{
		CID:      bktInfo.CID,
		Position: s.pos,
		Size:     s.size,
	}
	_, err := s.ng.TreeMove(ctx, desc, treeID, &pilorama.Move{
		Parent: parentID,
		Child:  nodeID,
		Meta: pilorama.Meta{
			Items: mapToKV(meta),
		},
	})
	return err
}

func (s treeServiceEngineWrapper) RemoveNode(ctx context.Context, bktInfo *data.BucketInfo, treeID string, nodeID uint64) error {
	if nodeID == pilorama.RootID {
		return fmt.Errorf("node with ID %d is the root and can't be removed", nodeID)
	}
	desc := pilorama.CIDDescriptor{
		CID:      bktInfo.CID,
		Position: s.pos,
		Size:     s.size,
	}
	_, err := s.ng.TreeMove(ctx, desc, treeID, &pilorama.Move{
		Parent: pilorama.TrashID,
		Child:  nodeID,
	})
	return err
}

func mapToKV(m map[string]string) []pilorama.KeyValue {
	var kvs []pilorama.KeyValue
	for k, v := range m {
		kvs = append(kvs, pilorama.KeyValue{
			Key:   k,
			Value: []byte(v),
		})
	}
	return kvs
}

func kvToTreeMeta(x []pilorama.KeyValue) []tree.Meta {
	ret := make([]tree.Meta, 0, len(x))
	for _, x := range x {
		ret = append(ret, kv{x.Key, x.Value})
	}
	return ret
}